The present disclosure relates to a ram air fan assembly. In particular, the disclosure relates to an inlet tube for a ram air fan assembly of an aircraft.
The environmental control system (“ECS”), including the ram air fan assembly, aboard an aircraft provides conditioned air to a cabin of the aircraft. Conditioned air is air at a desired temperature, pressure, and humidity for aircraft passenger comfort. Compressing ambient air at flight altitude heats the resulting pressurized air sufficiently that it must be cooled, even if the ambient air temperature is very low. Thus, under most conditions, heat must be removed from the air by the ECS before the air is delivered to the aircraft cabin. As heat is removed from the air, it is dissipated by the ECS into a separate stream of air that flows into the ram air fan assembly, across heat exchangers in the ram air fan assembly, and out of the aircraft, carrying the excess heat with it. Under conditions where the aircraft is moving fast enough, the pressure of air ramming into the aircraft is sufficient to move enough air through the ram air fan assembly and over the heat exchangers to remove the excess heat.
While ram air works well under normal flight conditions, at lower flight speeds, or when the aircraft is on the ground, ram air pressure is too low to provide enough air flow across the heat exchangers for sufficient heat removal from the ram air fan assembly.
Typically, ram air fan assemblies utilize an electric motor to drive the fan. This is accomplished by a rotor assembly, which is driven by a stator. The stator generates a significant amount of heat as a byproduct of the magnetic field used to drive the rotor assembly. Additionally, bearings that support the rotor assembly typically produce heat and, therefore, require cooling. As a result of these sources of heat, the electric motor must be cooled by sources such as external air. Thus, air is provided to the stator and bearings of the ram air fan along one or more flow paths from upstream or downstream of the ram air fan in the ECS.
Due to the collection inlet(s) location in the ECS (and the aircraft) adjacent the ram air fan assembly, the collection inlet(s) for cooling air are exposed to a high volume of particulate (such as dirt) during operation, which can result in foreign object damage (“FOD”). Thus, it is desirable to reduce the amount of particulate that reaches those components. Existing particle separators can be ineffective at removing particulate from cooling air as previous particle separators require a high velocity clean airstream, which may not be available at the ram air fan and the area there around. As a result, existing particle separators are subject to problems such as clogging or operate in an undesirable manner by introducing particle laden cooling air to interior components of the ram air fan. Additionally, existing particle separators do a good job of removing the FOD, however, they have a relatively large pressure drop due to the rapid change in air velocity, which tends to reduce the mass flow rate of cooling air passing through the motor.